Broadband parametric amplification for multiplexed SiMOS quantum dot signals

Spins in semiconductor quantum dots hold great promise as building blocks of quantum processors. Trapping them in SiMOS transistor-like devices eases future industrial scale fabrication. Among the potentially scalable readout solutions, gate-based dispersive radiofrequency reflectometry only requires the already existing transistor gates to readout a quantum dot state, relieving the need for additional elements. In this effort towards scalability, traveling-wave superconducting parametric amplifiers significantly enhance the readout signal-to-noise ratio (SNR) by reducing the noise below typical cryogenic low-noise amplifiers, while offering a broad amplification band, essential to multiplex the readout of multiple resonators. In this work, we demonstrate a 3GHz gate-based reflectometry readout of electron charge states trapped in quantum dots formed in SiMOS multi-gate devices, with SNR enhanced thanks to a Josephson traveling-wave parametric amplifier (JTWPA). The broad, tunable 2GHz amplification bandwidth combined with more than 10dB ON/OFF SNR improvement of the JTWPA enables frequency and time division multiplexed readout of interdot transitions, and noise performance near the quantum limit. In addition, owing to a design without superconducting loops and with a metallic ground plane, the JTWPA is flux insensitive and shows stable performances up to a magnetic field of 1.2T at the quantum dot device, compatible with standard SiMOS spin qubit experiments

Electrical manipulation of a single electron spin in CMOS using a micromagnet and spin-valley coupling

Les récentes avancées dans le domaine de l'information quantique ont donné un bel aperçu du potentiel qu'offre l'informatique quantique. Cependant, pour révéler toute la puissance d'un ordinateur quantique universel, des millions de qubits interconnectés sont nécessaires. Dans ce contexte, il semble naturel d'utiliser de la technologie complementary metal-oxide-semiconductor (CMOS) qui a rendu possible l'intégration de milliards de transistors dans les ordinateurs classiques. Les qubits de spin semi-conducteurs présentent de longs temps de cohérence, des fidélités élevées et peuvent être intégrés à l'aide de la technologie CMOS, ce qui en fait un candidat idéal pour une fabrication fiable et à large échelle. Il est difficile de passer directement d'une fabrication académique à des qubits entièrement fabriqués selon les normes CMOS industrielles sans solutions intermédiaires. La fabrication et la caractérisation de ces solutions intermédiaires sont donc au cœur de cette thèse.Tout d'abord, les propriétés matérielles pertinentes pour l'utilisation de qubits à basse température des dispositifs industrielle à base de fully depleted silicon-on-insulator (FD-SOI) sont étudiées. Les barres de Hall et les structures des boîtes quantiques sont utilisées pour la caractérisation. Des mesures de Hall à 400 mK, une densité de percolation d'environ 1*10^12 cm^-2 est extraite. Une mobilité maximale de (2350 +/- 20) cm^2/Vs est atteinte à une densité de (3.48 +/- 0.05)*10^12 cm^-2, probablement limitée par l'épaisseur de l'oxyde.Ensuite, un back-end-of-line (BEOL) flexible est introduit. Il permet de nouvelles fonctionnalités telles que des micro-aimants ou des circuits supraconducteurs qui peuvent être ajoutés dans une étape post-CMOS afin d'étudier la physique de ces dispositifs ou de réaliser une preuve de concept. Cette thèse étudie un qubit de spin à électron unique dans un dispositif CMOS avec un micro-aimant intégré dans le BEOL flexible. La relaxométrie révèle une séparation de vallée de l'ordre de 60 µeV et de longs temps de relaxation du spin autour de 400 ms.Des oscillations cohérentes utilisant la technique dite electric dipole spin resonance (EDSR) d'un spin d'électron unique avec des fréquences de Rabi autour de 1 MHz sont observées. La forme des oscillations de Rabi indique que la cohérence est limitée par le bruit à basse fréquence provenant des spins nucléaires restants dans le nanofil constitué de Si naturel.Le couplage spin-orbite synthétique (SOC) est exploité pour contrôler le qubit via des champs électriques et étudier la physique de la vallée de spin en présence de SOC où une augmentation de la fréquence de Rabi est montrée au point de dégnérescence de la vallée et du spin.Enfin, le bruit à haute fréquence dans le système est sondé en utilisant des séquences d'impulsions de découplage dynamique et il s'avère que le bruit de charge domine la décohérence du qubit dans cette gamme.Les travaux présentés dans cette thèse apportent la première preuve expérimentale de l'amélioration d’oscillations de Rabi avec la vallée et démontrent pour la première fois un qubit de spin électronique sur un substrat FD-SOI. La performance du qubit est comparable aux premières réalisations de qubits de spin sur d'autres plateformes de matériaux. L'introduction du 28Si devrait améliorer considérablement les propriétés de cohérence et l'EDSR assistée par la vallée pourrait permettre des vitesses de rotation plus rapides pour améliorer la qualité du qubit.Recent advances in quantum information gave a small insight into the potential quantum computing offers. To unveil the full power of a universal quantum computer however, millions of interconnected qubits are necessary. In this context, leveraging complementary metal-oxide-semiconductor (CMOS) technology that made the integration of billions of transistors in classical computers possible seems natural. Semiconductor spin qubits show long coherence times, high gate fidelities and they can be integrated using CMOS technology, which makes them an ideal candidate for reliable and scalable fabrication. The direct leap from academic fabrication to qubits fabricated fully by industrial CMOS standards is difficult to make without intermediate solutions. The fabrication and characterization of such intermediate solutions is at the heart of this thesis.First, the material properties relevant for qubit use at low temperatures of an industrial fully depleted silicon-on-insulator (FD-SOI) wafer are studied. Hall bars and quantum dot structures made by academic fabrication are used for characterization. From Hall measurements at 400 mK, a percolation density of around 1*10^12 cm^-2 is extracted. A peak mobility of (2350 +/- 20) cm^2/Vs is reached at a density of (3.48 +/- 0.05)*10^12 cm^-2, most likely limited by the oxide thickness.In a second step, a flexible back-end-of-line (BEOL) is introduced. It allows for new functionalities such as micro-magnets or superconducting circuits that can be added in a post-CMOS process to study the physics of these devices or achieve proof of concepts with the goal to incorporate the established process in the foundry-compatible process flow. In this thesis, a single electron spin qubit in a CMOS device with a micro-magnet integrated in the flexible BEOL is studied. Relaxometry reveals a valley-splitting in the order of 60 µeV and long spin relaxation times around 400 ms. Coherent oscillations using electric dipole spin resonance (EDSR) of a single electron spin with Rabi frequencies around 1 MHz are observed. The shape of the Rabi oscillations indicates that the coherence is limited by low frequency noise originating from the remaining nuclear spins in the natural Si channel.The synthetic spin-orbit coupling (SOC) is exploited to control the qubit via electric fields and investigate the spin-valley physics in the presence of SOC where an enhancement of the Rabi frequency is shown at the spin-valley hotspot.Finally, the high frequency noise in the system is probed using dynamical decoupling pulse sequences and charge noise is found to dominate the qubit decoherence in this range.The work presented in this thesis provides first experimental evidence for valley enhanced EDSR and demonstrates an electron spin qubit on a FD-SOI substrate for the first time. The qubit performance is comparable to early spin qubit realizations on other material systems. The introduction of isotopically purified 28Si is expected to greatly improve the coherence properties and valley enhanced EDSR may enable faster driving speeds for improved qubit quality

Manipulation électrique d'un spin d'électron unique dans CMOS à l'aide d'un micro-aimant et d'un couplage spin-vallée

Recent advances in quantum information gave a small insight into the potential quantum computing offers. To unveil the full power of a universal quantum computer however, millions of interconnected qubits are necessary. In this context, leveraging complementary metal-oxide-semiconductor (CMOS) technology that made the integration of billions of transistors in classical computers possible seems natural. Semiconductor spin qubits show long coherence times, high gate fidelities and they can be integrated using CMOS technology, which makes them an ideal candidate for reliable and scalable fabrication. The direct leap from academic fabrication to qubits fabricated fully by industrial CMOS standards is difficult to make without intermediate solutions. The fabrication and characterization of such intermediate solutions is at the heart of this thesis.First, the material properties relevant for qubit use at low temperatures of an industrial fully depleted silicon-on-insulator (FD-SOI) wafer are studied. Hall bars and quantum dot structures made by academic fabrication are used for characterization. From Hall measurements at 400 mK, a percolation density of around 1*10^12 cm^-2 is extracted. A peak mobility of (2350 +/- 20) cm^2/Vs is reached at a density of (3.48 +/- 0.05)*10^12 cm^-2, most likely limited by the oxide thickness.In a second step, a flexible back-end-of-line (BEOL) is introduced. It allows for new functionalities such as micro-magnets or superconducting circuits that can be added in a post-CMOS process to study the physics of these devices or achieve proof of concepts with the goal to incorporate the established process in the foundry-compatible process flow. In this thesis, a single electron spin qubit in a CMOS device with a micro-magnet integrated in the flexible BEOL is studied. Relaxometry reveals a valley-splitting in the order of 60 µeV and long spin relaxation times around 400 ms. Coherent oscillations using electric dipole spin resonance (EDSR) of a single electron spin with Rabi frequencies around 1 MHz are observed. The shape of the Rabi oscillations indicates that the coherence is limited by low frequency noise originating from the remaining nuclear spins in the natural Si channel.The synthetic spin-orbit coupling (SOC) is exploited to control the qubit via electric fields and investigate the spin-valley physics in the presence of SOC where an enhancement of the Rabi frequency is shown at the spin-valley hotspot.Finally, the high frequency noise in the system is probed using dynamical decoupling pulse sequences and charge noise is found to dominate the qubit decoherence in this range.The work presented in this thesis provides first experimental evidence for valley enhanced EDSR and demonstrates an electron spin qubit on a FD-SOI substrate for the first time. The qubit performance is comparable to early spin qubit realizations on other material systems. The introduction of isotopically purified 28Si is expected to greatly improve the coherence properties and valley enhanced EDSR may enable faster driving speeds for improved qubit quality.Les récentes avancées dans le domaine de l'information quantique ont donné un bel aperçu du potentiel qu'offre l'informatique quantique. Cependant, pour révéler toute la puissance d'un ordinateur quantique universel, des millions de qubits interconnectés sont nécessaires. Dans ce contexte, il semble naturel d'utiliser de la technologie complementary metal-oxide-semiconductor (CMOS) qui a rendu possible l'intégration de milliards de transistors dans les ordinateurs classiques. Les qubits de spin semi-conducteurs présentent de longs temps de cohérence, des fidélités élevées et peuvent être intégrés à l'aide de la technologie CMOS, ce qui en fait un candidat idéal pour une fabrication fiable et à large échelle. Il est difficile de passer directement d'une fabrication académique à des qubits entièrement fabriqués selon les normes CMOS industrielles sans solutions intermédiaires. La fabrication et la caractérisation de ces solutions intermédiaires sont donc au cœur de cette thèse.Tout d'abord, les propriétés matérielles pertinentes pour l'utilisation de qubits à basse température des dispositifs industrielle à base de fully depleted silicon-on-insulator (FD-SOI) sont étudiées. Les barres de Hall et les structures des boîtes quantiques sont utilisées pour la caractérisation. Des mesures de Hall à 400 mK, une densité de percolation d'environ 1*10^12 cm^-2 est extraite. Une mobilité maximale de (2350 +/- 20) cm^2/Vs est atteinte à une densité de (3.48 +/- 0.05)*10^12 cm^-2, probablement limitée par l'épaisseur de l'oxyde.Ensuite, un back-end-of-line (BEOL) flexible est introduit. Il permet de nouvelles fonctionnalités telles que des micro-aimants ou des circuits supraconducteurs qui peuvent être ajoutés dans une étape post-CMOS afin d'étudier la physique de ces dispositifs ou de réaliser une preuve de concept. Cette thèse étudie un qubit de spin à électron unique dans un dispositif CMOS avec un micro-aimant intégré dans le BEOL flexible. La relaxométrie révèle une séparation de vallée de l'ordre de 60 µeV et de longs temps de relaxation du spin autour de 400 ms.Des oscillations cohérentes utilisant la technique dite electric dipole spin resonance (EDSR) d'un spin d'électron unique avec des fréquences de Rabi autour de 1 MHz sont observées. La forme des oscillations de Rabi indique que la cohérence est limitée par le bruit à basse fréquence provenant des spins nucléaires restants dans le nanofil constitué de Si naturel.Le couplage spin-orbite synthétique (SOC) est exploité pour contrôler le qubit via des champs électriques et étudier la physique de la vallée de spin en présence de SOC où une augmentation de la fréquence de Rabi est montrée au point de dégnérescence de la vallée et du spin.Enfin, le bruit à haute fréquence dans le système est sondé en utilisant des séquences d'impulsions de découplage dynamique et il s'avère que le bruit de charge domine la décohérence du qubit dans cette gamme.Les travaux présentés dans cette thèse apportent la première preuve expérimentale de l'amélioration d’oscillations de Rabi avec la vallée et démontrent pour la première fois un qubit de spin électronique sur un substrat FD-SOI. La performance du qubit est comparable aux premières réalisations de qubits de spin sur d'autres plateformes de matériaux. L'introduction du 28Si devrait améliorer considérablement les propriétés de cohérence et l'EDSR assistée par la vallée pourrait permettre des vitesses de rotation plus rapides pour améliorer la qualité du qubit

Probing Low-Frequency Charge Noise in Few-Electron CMOS Quantum Dots

International audienceCharge noise is one of the main sources of environmental decoherence for spin qubits in silicon, presenting a major obstacle in the path towards highly scalable and reproducible qubit fabrication. Here we demonstrate in-depth characterization of the charge noise environment experienced by a quantum dot in a CMOS-fabricated silicon nanowire. We probe the charge noise for different quantum dot configurations, finding that it is possible to tune the charge noise over two orders of magnitude, ranging from 1μeV2/Hz to 100μeV2/Hz. In particular, we show that the top interface and the reservoirs are the main sources of charge noise, and their effect can be mitigated by controlling the quantum dot extension. Additionally, we demonstrate a method for the measurement of the charge noise experienced by a quantum dot in the few-electron regime. We measure a comparatively high charge noise value of 40μeV2/Hz at the first electron, and demonstrate that the charge noise is highly dependent on the electron occupancy of the quantum dot

Parity and singlet-triplet high fidelity readout in a silicon double quantum dot at 0.5 K

We demonstrate singlet-triplet readout and parity readout allowing to distinguish T0 and the polarized triplet states. We achieve high fidelity spin readout with an average fidelity above $99.9\%$ for a readout time of $20~\mu$s and $99\%$ for $4~\mu$s at a temperature of $0.5~K$. We initialize a singlet state in a single dot with a fidelity higher than $99\%$ and separate the two electrons while keeping the same spin state with $a \approx 95.6\%$ fidelity

Broadband parametric amplification for multiplexed SiMOS quantum dot signals

International audienceSpins in semiconductor quantum dots hold great promise as building blocks of quantum processors. Trapping them in SiMOS transistor-like devices eases future industrial scale fabrication. Among the potentially scalable readout solutions, gate-based dispersive radiofrequency reflectometry only requires the already existing transistor gates to readout a quantum dot state, relieving the need for additional elements. In this effort towards scalability, traveling-wave superconducting parametric amplifiers significantly enhance the readout signal-to-noise ratio (SNR) by reducing the noise below typical cryogenic low-noise amplifiers, while offering a broad amplification band, essential to multiplex the readout of multiple resonators. In this work, we demonstrate a 3GHz gate-based reflectometry readout of electron charge states trapped in quantum dots formed in SiMOS multi-gate devices, with SNR enhanced thanks to a Josephson traveling-wave parametric amplifier (JTWPA). The broad, tunable 2GHz amplification bandwidth combined with more than 10dB ON/OFF SNR improvement of the JTWPA enables frequency and time division multiplexed readout of interdot transitions, and noise performance near the quantum limit. In addition, owing to a design without superconducting loops and with a metallic ground plane, the JTWPA is flux insensitive and shows stable performances up to a magnetic field of 1.2T at the quantum dot device, compatible with standard SiMOS spin qubit experiments

Broadband parametric amplification for multiplexed SiMOS quantum dot signals

International audienceSpins in semiconductor quantum dots hold great promise as building blocks of quantum processors. Trapping them in SiMOS transistor-like devices eases future industrial scale fabrication. Among the potentially scalable readout solutions, gate-based dispersive radiofrequency reflectometry only requires the already existing transistor gates to readout a quantum dot state, relieving the need for additional elements. In this effort towards scalability, traveling-wave superconducting parametric amplifiers significantly enhance the readout signal-to-noise ratio (SNR) by reducing the noise below typical cryogenic low-noise amplifiers, while offering a broad amplification band, essential to multiplex the readout of multiple resonators. In this work, we demonstrate a 3GHz gate-based reflectometry readout of electron charge states trapped in quantum dots formed in SiMOS multi-gate devices, with SNR enhanced thanks to a Josephson traveling-wave parametric amplifier (JTWPA). The broad, tunable 2GHz amplification bandwidth combined with more than 10dB ON/OFF SNR improvement of the JTWPA enables frequency and time division multiplexed readout of interdot transitions, and noise performance near the quantum limit. In addition, owing to a design without superconducting loops and with a metallic ground plane, the JTWPA is flux insensitive and shows stable performances up to a magnetic field of 1.2T at the quantum dot device, compatible with standard SiMOS spin qubit experiments

Parity and singlet-triplet high fidelity readout in a silicon double quantum dot at 0.5 K

International audienceWe demonstrate singlet-triplet readout and parity readout allowing to distinguish T0 and the polarized triplet states. We achieve high fidelity spin readout with an average fidelity above $99.9\%$ for a readout time of $20~\mu$s and $99\%$ for $4~\mu$s at a temperature of $0.5~K$. We initialize a singlet state in a single dot with a fidelity higher than $99\%$ and separate the two electrons while keeping the same spin state with $a \approx 95.6\%$ fidelity

Parity and Singlet-Triplet High-Fidelity Readout in a Silicon Double Quantum Dot at 0.5 K

Pauli-spin-blockade (PSB) measurements have so far achieved the highest fidelity of spin readout in semiconductor quantum dots, overcoming the 99% threshold. Moreover, in contrast to energy-selective readout, PSB is less error prone to thermal energy, an important feature for large-scale architectures that could be operated at temperatures above a few hundreds of millikelvins. In this work, we use rf reflectometry on a single-lead quantum dot to perform charge sensing and to probe the spin state of a double quantum dot at 0.5 K. At this relatively elevated temperature, we characterize both singlet-triplet and parity readout, which are complementary measurements to perform a complete readout of a two-spin system. We demonstrate high-fidelity spin readout with an average fidelity above 99.9 % for a readout time of 20 µs and 99 % for 4 µs. Finally, we succeed in initializing a singlet state in a single dot with a fidelity higher than 99 % and separate the two electrons while retaining the same spin state with a 95.6 % fidelity

Electrical manipulation of a single electron spin in CMOS with micromagnet and spin-valley coupling

International audienceFor semiconductor spin qubits, complementary-metal-oxide-semiconductor (CMOS) technology is the ideal candidate for reliable and scalable fabrication. Making the direct leap from academic fabrication to qubits fabricated fully by industrial CMOS standards is difficult without intermediate solutions. With a flexible back-end-of-line (BEOL) new functionalities such as micromagnets or superconducting circuits can be added in a post-CMOS process to study the physics of these devices or achieve proof of concepts. Once the process is established it can be incorporated in the foundry-compatible process flow. Here, we study a single electron spin qubit in a CMOS device with a micromagnet integrated in the flexible BEOL. We exploit the synthetic spin orbit coupling (SOC) to control the qubit via electric field and we investigate the spin-valley physics in the presence of SOC where we show an enhancement of the Rabi frequency at the spin-valley hotspot. Finally, we probe the high frequency noise in the system using dynamical decoupling pulse sequences and demonstrate that charge noise dominates the qubit decoherence in this range